The Energy Independence & Security Act of 2007 (EISA) set minimum efficiency standards for many of the common incandescent lamps, and these standards go into effect during subsequent years. Many incandescent lamps, including the A-line incandescent lamps with medium screw bases that have become commonplace in residential and amenity areas, do not have sufficiently high luminous efficacies, defined as lumens per watt (LPW), to meet these new efficiency standards. Compact fluorescent lamps are one technical solution for providing replacement lamps with sufficient luminous efficacies. However, consumers do not desire the color of the compact fluorescent lamps. As a result, the lamps have not been greeted with enthusiasm in the marketplace.
Modified Spectrum General Service incandescent lamps, hereinafter referred to as “modified spectrum lamps,” are a category of lamps defined by EISA. According to the definition, such modified spectrum lamps have desirable color properties for general lighting purposes but they are not sufficiently saturated in color to be classified in the defined category of Colored Lamps. EISA requires that the modified spectrum lamps not be more than about 25% below the LPW requirements for the category of General Service Incandescent Lamps.
EISA provides the lumen requirements for General Service Incandescent Lamps and Modified Spectrum Incandescent Lamps. For example, a 72 Watt General Service Incandescent Lamp needs to have 1490-2600 lumens. Accordingly, a 72 Watt Modified Spectrum Incandescent Lamp needs to have 1118-1950 lumens.
There are several commercially available A-line incandescent lamps in the Modified Spectrum class at the present, for example GE Reveal®, Philips Natural Light™, and Osram Sylvania Living Spaces™. These are conventional gas-filled incandescent lamps with either a tinted bulb glass or a tinted internal powder coating to cause slight deviations in the spectra of the light after it has been emitted directly from the filament. Chromaticity ranges of these lamps are shown in FIG. 1 on a 1931 CIE chromaticity diagram.
The GE Reveal lamps are based on the absorption of neodymium. Introduction of neodymium causes the color temperature (CT) of the filament-emitted light to increase with small neodymium concentrations. At sufficiently large neodymium concentrations, the CT decreases but the efficacy losses become unreasonable. The chromaticity is well below the blackbody locus meaning that the lamps have magenta tints.
Conversely, Osram Sylvania Living Spaces and Philips Natural Light lamps increase the CT of the filament-emitted light with reasonable increases of colorant concentration. The chromaticity remains closer to the blackbody locus meaning that the light does not take on the magenta tint associated with the neodymium lamps. A principle visual characteristic of the light from these lamps is that it tends to look somewhat less yellowish than the direct filament-emitted light. Such lamps tend to be more flattering to human complexion than compact fluorescent lamps. In addition, the lamps render a generally preferred appearance of objects with strong red reflective properties, i.e., where the spectral reflectance curve is high at wavelengths above about 620 nm.
These lamps have an undesirable feature that the color temperature is above the color temperature of comparable wattage of standard incandescent lamps. The color temperature range of standard incandescent lamps is usually considered to be the desirable range for residential and amenity applications. Lower color temperature may often be preferred. Furthermore, for residential and amenity applications the appearance of warmth is usually desirable where the lower color temperatures tend to be more flattering to human appearance. Other psychological factors, such as those used to evaluate quantitatively color preference for light sources, also are involved in explaining such desires and preferences.